L10 PALAEONTOLOGY OF NEW YORK. 



Interior unknown. 



Ligamental area with one or two longitudinal grooves. 



The specimen lias a length of IS mm., height lti mm. 



Formation and locality. In the Marcellus shale at East Bloomfield, Ontario 

 county, N. Y. 



AcTINOPTEBIA SUBDEOUSSATA. 

 PLATE XVII, FIGS. 83, 25-27, 29-31; ami PLATE XIX. PIG. 25. 



Ptertmites siibdecussata, Hall. Ms., vol. v. IS77. 



S. A. Miller in Cat. Am. Pal. Fuss., p. 202. 1877. 

 Actinopteria ttuMteuxsaia, Hall. Pal. N. V.. vol. v, pt. 1. Plat.-s and Explanations: PI. 17. figs. 33, 25- 



27. 29-31 : pi. 19, fig. 25. .Ian.. 1883. 



Shell large, suh-rhomboidal, very oblique; body elongate sub-ovate ; height 

 about one-third less than the length ; margins regularly curved, becoming 

 more extended on the posterior side. 



The left valve, in old specimens, has the umbo convex above, depressed- 

 convex or Mat below, while in young specimens the umbo is altogether eon- 

 vex or gibbous. Right valve moderately convex near the umbo. Hat or 

 concave below the middle. 



Hinge-line straight, length about one-fifth less than the length of the shell, 

 not extending as tar as the posterior margin of the left valve, but extending 

 beyond the posterior margin of the right valve. 



Beak acute, directed forward, somewhat prominent, anterior nearly 

 terminal. Umbonal region (in young shells) well marked by the sulci; 

 umbonal angle acute. 



Ear very small, separated by a vertical sulcus. Wing large, triangular, 

 defined in young shells by the abrupt convexity of the post-cardinal slope;- 

 in old specimens not distinctly defined ; margin concave; extremity acute. 

 The wing of the right valve is larger, and extends beyond the margin of the 

 shell. 



Test comparatively thin, marked with regular, sub-angular, alternating radii, 

 the stronger ones extending from the summit of the umbo; a second set interca- 



